What causes cerebral edema post radiation?

Hi All,

I know cerebral edema is a complication or side effect of any kind of radiation treatment but does anyone knows what causes it or send me a link for a good website which explains it. I tried googling it but couldn't find the exact reason.

Radiation necrosis is one of the reasons of cerebral edema but as per my knowledge that happens after a few years of radiation, isn't that correct?

The reason i ask this question is - I had cerebral edema since almost the start of the year(GK recd oct last yr) and every time it exposed itself with different symptoms - slurred speech, headaches, righthand drop(my AVM is left frontal). I'm on steroids since August now and having significant side effects...so want to quickly taper off but my neurosurgeon dont want to do that as he fears that edema might come back so it becomes a balancing act..but what is causing it(as I'm weaning off my headaches are coming back)and for how long it'll continue, I know everyone reacts to radiation treatment differently depending on size/location of their AVM but if people can share their experience it'd be useful as well..Im just over the 1 yr mark now of GK.

Thanks.